This invention relates generally to the field of refrigeration and cooling devices, and more particularly to the field of devices used to provide conditioned air to a space.
Conventional air conditioning devices employ a refrigeration cycle that harnesses the cooling effect accompanying evaporation of a fluid within a closed environment. Ordinarily, this fluid has been a liquid, and that simple fact has long prompted the art to seek a workable method for air conditioning using air itself as the cooling medium. The recognition that conventional refrigerants may pose environmental hazards, and the resulting regulation of fluids such as the CFC and HCFC families of refrigerants, has intensified that search.
The basic facts have been known for some time. The process for directly cooling air is delineated in the so-called "reverse Brayton cycle" (or "air cycle"), which describes the thermodynamic process of compressing air, rejecting the heat of compression, and then expanding the air to cool it below its starting temperature. Applying this theoretical knowledge has proved difficult, however.
The most promising development by the prior art has been the series of patents issued to Thomas C. Edwards and his co-workers, beginning with U.S. Pat. No. 3,686,893 in 1972. This voluminous collection of patents discloses a cooling system based on a rotary vane compressor-expander. In general, Edwards envisioned a rotary vane device carried in an elliptical housing, in which vane travel is controlled by rollers actuated by various camming arrangements carried in the end plates of specific embodiments. Inlet and outlet ports, are provided, often with provisions for controlling noise produced by pressure differentials (e.g., U.S. Pat. No. 3,905,204) or with provision for adding moisture to the air (e.g., U.S. Pat. No. 4,017,285). The geometry of the compressor-expander body is not generally addressed, but in U.S. Pat. No. 4,086,426, the structure is disclosed as elliptical, with the elliptical eccentricity of the expander side being slightly less than that of the compressor side of the device. Various others of these patents address particular aspects of this system, such as controlling vane travel (e.g., U.S. Pat. No. 3,886,764), providing a low-friction bearing surface for the vane (e.g., U.S. Pat. No. 3,904,327), and similar features.
After more than twenty years of development, however, no successful commercial embodiment of the Edwards inventions has been introduced. The inherent complexity of these devices, as seen in the patents, may have prevented the development of embodiments that could effectively compete in the marketplace. Thus, the art still awaits a device that can employ air cycle cooling in a manner that is not only effective but is also economically feasible. That is precisely the result achieved by the present invention.